Isolated bridge topologies such as the half-bridge (HB) or full-bridge (FB) can be paired with different rectifier configurations. The selection of rectifier configurations depends on the requirements of the design, including output voltage and current requirements. The current doubler ectifier uses a single secondary winding coupled with two inductors, while maintaining the equivalent voltage stress of a full-wave rectifier. Each inductor is energized once per positive or negative cycle of the switching period, and therefore require symmetrical pulses to balance current in both branches of the doubler. Accordingly, current doubler rectifiers are not typically used for powering systems with very dynamic load conditions, such as CPU (central processing unit) applications. Also, to obtain high efficiency, high value inductors often with lower saturation limits are conventionally used so the current imbalance during (dynamic) load transients may cause inductor saturation.
Current doubler rectifiers are beneficial in high power applications with limited load activity, such that fast dynamic response is not a primary concern. In such systems, the extra magnetic components are justifiable from an area and cost perspective. Further, with infrequent load transients, balancing the inductor currents is not a consideration. However, when used in lower power applications such as powering CPUs, handling the load transient while balancing the inductor currents is preferred to avoid saturation of one of the inductors and at the same time achieve faster transient response. One way to maintain current balance during a transient load condition is to lock the duty cycle for the primary side during each half cycle. However, the transient response becomes sluggish because the reaction time is up to one switching period. Accordingly, an improved control technique for isolated power converters during transient load conditions is needed.